Method of making mandrels



June 17, 1947. s, ACEK' 2,422,500 2 METHOD QF MAKING MANDRELS Fild July 19, 1945 Fig.2.

2 Inventor Steven D. Poliacek,

H s Attorney.

ture of mandrels.

Patented June 17, 1947 METHOD OF MAKING MANDRELS Steven D. Poliacek, Detroit, Mich assignor to Carboloy Company, Ine., Detroit, Mich a corporation of New York Application July 19, 1945, Serial No. 606,002

3 Claims. 1

The present invention is a method of makin a mandrel suitable for use in drawing metal tubing and the like and particularly a mandrel in which the wear ring or work portion of the mandrel is a hard metal composition, for example a cemented carbide consisting of a sintered mixture of one or more carbides with a lower melting point binder metal.

Prior to the present invention mandrels employed in the production of tubing generally consisted of a wear ring mechanically held onto various lengths of steel rod over which the tubing was pulled. Such mandrels usually have consisted of a steel shank provided at one end with a screw-threaded hole adapted to receive a bolt having a screw-threaded end portion adapted to engage the screw threaded opening in the steel shank. The screw-threaded bolt was provided with a head and a'tapered portion intermediate the head and screw-threaded end portion. A cemented carbide wear ring having a tapered hole corresponding to the taper on the bolt was positioned thereon. When the mandrel was assembled the cemented carbide wear ring was firmly seated against the outer end of the steel shank and on the tapered portion of the bolt.

The outside diameter of drawn tubin is determined by the die while its inside diameter is determined by the mandrel. The method heretofore employed in constructing tube drawing mandrels constitutes exacting and highly skilled operations. For example, on many tube drawing operations it is necessary to hold dimensions to two ten-thousandths of an inch and if the wear ring is lapped too much it immediately becomes oversize and is scrapped. In addition, the inner surface of the wear rings must have a precision lapped surface over its entire length so that it will contact with the steel bolt which secures it to the end of the steel shank. Otherwise outside pressure on the wear ring will tend to crack it due to lack of proper backing support.

It is an object of the present invention to simplify the construction of tube-drawing mandrels employing cemented carbide or other hard metal work rings. It is a further object of the invention to eliminate the expensive lapping and fitting operations heretofore employed. in the manufac- A further object is the provisions of a mandrel having an unusually long life. Other objects will appear hereinafter.

The novel features which are characteristic of my invention are set forth with particularity in the appended claims. My invention itself however will best be understood from reference to the following specification when considered in connection with the accompanying drawing in which Fig. 1 is a cross section of the outemend portion of a tube drawing mandrel embodying the features of the present invention; Fig. 2 is a view partly in section and partly in elevation illustrating steps in the manufacture of the mandrel disclosed in Fig. 1; while Fig. 3 is a cross sectional view of the end portion of the mandrel before it is machined to final form.

Referring more particularly to the drawing, I have indicated at l a steel bar or shank having a reduced diameter integral extension or stud 2 on one end thereof. A cemented carbide wear ring 3, the inner surface of which is tapered slightly is positioned on the stud 2 and against the shoulder t on the shank l; The outer surface of ring 3 usually is tapered slightly the diameter increasing'from the outer to the inner end of the ring 3. The diameter of the stud 2 is substantially equal to the smallest diameter of the hole through the Wear ring 3 while the outer diameter of the wear ring 3 at the point of contact with shank i is the same as the diameter of the steel shank A steel cap 5 is positioned on stud 2 and against the outer end of the wear ring 3. The cap 5 has a counterbored portion 6.

After the wear ring 3 and cap 5 have been positioned on the stud 2 of the shank i the assembled parts are heated in any suitable manner to a temperature of about 2050 F. and placed in a heavy split steel holder 1 having recessed or relief portions 8 and 9 and then forged. The forging operation is effected by pressure applied by a hammer It or other suitable means which forces the hot metal in the stud 2 to fill the entire opening in the wear ring 3 as well as the counterbored portion 6 in the steel cap 5.

The forging operation leaves an excess quantity of metal ii on the end of the mandrel as indicated in Fig. 3 of the drawing; When the forging operation is complete the mandrel is removed from the holder l and the excess metal ii removed from the stud 2. The cap 5 is then machined to provide it with the desired taper. At the same time the outer edge of the wear ring 5 is beveled slightly at its point of contact with the cap 5 as indicated at E2 in Fig. l. Countersunk portions i3 on the ends of the mandrel facilitate the machining operation.

In the use of tube drawing mandrels the tubing is pulled over the mandrel from the shank end. In prior art mandrels in which the wear ring is held by mechanical means, such as a screw bolt,

the wear ring has a tendency to pull away from 3 the shank in the drawing operation and to snap back when the operation is completed thereby causing chipping and breakage in the ring. This defect is eliminated in my improved mandrel.

Little, if any, skilled labor is required in th'e construction of my improved mandrel since all lapping and fitting operations hitherto employed are eliminated. Moreover, it is easy to assemble and owing to its method of manufacture it is strong and rugged and free from defects due to insufflcient backing support. Since about 75% of the necessary precision work involved in the construction of prior art mandrels is unnecessary in my process, the cost of manufacturing my improved mandrel is far less than the cost of manufacturing mandrels employinga mechanical holding means such as a threaded bolt.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The method of making a tube drawing mandrel consisting of a steel shank, a cemented ca'rbide wear ring and an annealed steel cap which comprises providing the steel shank with an integral reduced extension or stud, positioning said ring and cap in that order on said stud, said ring and cap each having tapered inner surfaces, the degree of taper on said cap being substantially greater than the degree of taper on said ring, heating said stud to an elevated temperature and forging it to'thereby force the metal therein into intimate contact with said wear ring and cap.

2. The method of making a tube drawing mandrel comprising a steel shank, a cemented carbide wear ring and a steel cap which comprises providing the steel shank with a reduced extension or stud, forming a tapered inner surface on said wear ring the smallest diameter of which is substantially equal to the diameter of said stud, positioning said wear ring on said stud with the end having the smallest diameteropening in contact with said shank, forming a counterbored portion on the outer nd of the steel cap, positioning said cap on said stud and against said wear ring, heating the stud to an elevated temperature and tioning said wear ring on said stud with the end forging said stud so as to flll'th'e tapered opening in the wear ring and the counterbored portion of said cap, thereafter removing excess metal from the outer end of said forged stud and shaping the steel cap to provide it with a desired outer surface.

3. The method of making a tube drawing man-- drel comprising a steel shank, a cemented carbide wear ring and a steel cap which comprises providing the steel shank with a reduced extension or stud, forming a tapered inner surface on said wear ring the smallest diameter of which is substantially equal to the diameter of said ,stud, posihaving the smallestdiameter opening in contact with said shank, forming a counterbored portion on the outer end of the steel cap, positioning said cap on said stud and against said wear ring, heating the stud to an elevated temperature and forging said stud so as to flllvthe tapered opening in the wear ring and-the counterbored portion of said cap.

STEVEN D. POLIACEK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

